The dangers of laser eye surgery are not being properly explained to people desperate to improve their vision.
One in three consultations by clinics offering the treatment were of poor quality, according to a Which? investigation.
The consumer watchdog found that the relatively low prices promised by the major chains in their marketing are not what they seem, while some outlets sting customers with unexpected fees.
Painfully dry eyes can occur as a result of damage to the nerves that stimulate tears, while damage to the rim of the eyelids can also result in painful ingrowing eyelashes, which must be plucked several times a month by an optician.
Which? said that good written information was provided at all of the clinics but many fell down on explaining details of the risks.
The group said: "Serious long-term complications are rare but in extreme cases patients can have long-term problems, such as severe dry eyes, so it is important people are aware of this before they commit."